1. Technical Field
This disclosure relates to pumps for cooking oil and, more specifically, pumps for delivering unsaturated and/or non-trans-fat cooking oils. Still more specifically, this disclosure relates to improved pump and seal mechanisms for pumps intended to deliver cooking oils. The disclosed seal mechanisms and pump designs provide improved wear characteristics and therefore require less maintenance and longer operating times between servicing and replacements than existing seal mechanisms. Further, this disclosure relates to pumps and distribution systems for filtering and recirculating oil and for adding fresh oil to deep oil fryers using a single motor.
2. Description of the Related Art
Trans-fat is the common name for a type of unsaturated fat with trans-isomer fatty acid(s). Trans-fats may be monounsaturated or polyunsaturated. Most trans-fats consumed today are created industrially through partial hydrogenation of plant oils through a process developed in the early 1900s. The goal of partial hydrogenation is to add hydrogen atoms to unsaturated fats, making them more saturated, i.e. fewer double bonds between carbon atoms. These more saturated fats have a higher melting point, which makes them attractive for baking and extends their shelf-life. For example, the hydrogenated vegetable oil or trans-fat added to shelf-stable peanut butter that replaces natural peanut oil enables such shelf-stable peanut butters to be stored without refrigeration and without the trans-fat separating from the other components of the peanut butter. In contrast, natural peanut butters have shorter shelf lives and the peanut oil naturally separates from the heavier components of peanut butter.
Unlike other dietary fats, trans-fats are neither essential nor even nutritious. In fact, the consumption of trans-fats increases the risk of coronary heart disease by raising levels of “bad” LDL cholesterol and lowering levels of “good” HDL cholesterol. Health authorities worldwide recommend that consumption of trans-fat be reduced to trace amounts. In sum, trans-fats from partially hydrogenated oils are widely regarded as being less healthy than naturally occurring oils.
Chemically, trans-fats are made of the same building blocks as non-trans-fats, but have a different arrangement. In trans-fatty acid molecules, the hydrogen atoms bonded to pairs of double-bonded carbon atoms (characteristic of all unsaturated fats) are in the trans rather than the cis molecular arrangement. This results in a straight, rather than kinked, shape for the carbon chain, more like the straight chain of a fully saturated fat. The trans and cis versions of a fatty acid having the same chemical formula have different chemical and physical properties owing to the slightly different bond configuration. Notably, the trans-fat has a much higher melting point, due to the ability of the trans molecules to pack more tightly, forming a solid that is more difficult to break apart and that it is a solid at human body temperatures.
Prior to 2006, Americans consumers could not determine the quantity of trans-fats in food products. This information could only be inferred from the ingredient list, notably from the partially hydrogenated ingredients. According to the FDA, the average American consumes 5.8 grams of trans-fat per day or about 2.6% of an average caloric intake. On Jul. 11, 2003, the FDA issued a regulation requiring manufacturers to list the trans-fat content on food labels. However, unlike many other countries, trans-fat levels of less than 0.5 grams per serving can be listed as 0 grams trans-fat on the food label. Though this is a small amount, multiple servings can exceed recommended levels. Thus, many consumers do not know how to interpret the meaning of trans-fat content on the nutrition facts panel. In fact, without specific prior knowledge about trans-fat and its negative health effects, consumers, including those at risk for heart disease, may misinterpret nutrient information provided on the panel. However, there is no requirement to list trans-fats on institutional food packaging, thus bulk purchasers like schools, hospitals, and cafeterias are unable to evaluate the trans-fat content of commercial food items.
The FDA defines trans-fats as containing one or more trans linkage that are not in a conjugated system. This is an important distinction, as it distinguishes non-conjugated synthetic trans-fats from naturally occurring fatty acids with conjugated trans double bonds, such as conjugated linoleic acid.
Critics of the FDA have expressed concern that the 0.5 gram per serving threshold is too high to refer to a food as free of trans-fat and that consumers should be warned about the presence of naturally occurring trans-fats in processed foods. Some US cities are independently acting to reduce consumption of trans-fats with public education campaigns and requests to restaurant owners to voluntarily eliminate trans-fat from their offerings.
Therefore, pressure from consumers and public health advocates to convert from cooking oils containing trans-fats to cooking oils free of trans-fats is present now and will only increase in the future. It is anticipated that corn, soybean and canola oils will be the primary substitutes for trans-fat oils.
Deep fryers are a necessity of the food service industry and particularly for the fast food service industry. Deep fryers use a substantial amount of shortening or oil during the cooking process. During the cooking process much of the oil is absorbed by a food product, resulting in loss of oil volume. The remaining oil can become filled with debris due to constant use. Accordingly, as more expensive oils that are free of trans-fats are being used, there is a need to extend the usable life of the unabsorbed oil and to keep the unused oil clean during the cooking process. Accordingly, there is a need for a deep fryer that efficiently filters used oil.
Further, with respect to hot oil or “deep” fryers, improved pump designs are needed as manufactures replace trans-fat oils with zero trans-fat oils. More specifically, a typical deep fryer requires at least two pumps: first, a filter/return pump for drawing used cooking oil from the cooking vat through a filter system and then pumping the filtered oil back into the cooking vat; and second, a supply pump for “topping-off” the cooking vat with clean or fresh oil as the oil level in the vat decreases. However, many deep fryers include multiple cooking vats. As a result, the distribution system to direct the flow from the filter/return and supply pumps to the various cooking vats of a typical deep fryer is complex and cumbersome.
Further, currently available pumps, used for use in food manufacturing and in food preparation, are prone to frequent seal failure when used to pump natural, unsaturated and trans-fat-free oils such as corn, soybean and canola oils. For example, pumps are used in hot oil filtration process of deep fryers used in the manufacturing or preparation of French fries, fish, and chicken. During the transition between trans-fat oils and zero trans-fat oils, it has been found that seal failure has become commonplace. Accordingly, an improved seal design for pumps intended for pumping a hot trans-fat-free oils is needed and a seal design that particularly avoids the use of the currently employed material—fluoropolymer elastomers or fluoroelastomers.
Fluoroelastomers are commonly used in O-rings and other molded or extruded goods. Fluoroelastomers are part of a family comprising copolymers of hexafluoropropylene (HFP) and vinylidene fluoride (VDF or VF2), terpolymers of tetrafluoroethylene (TFE), vinylidene fluoride (VDF) and hexafluoropropylene (HFP) as well as perfluoromethylvinylether (PMVE) containing specialties. The fluorine content of the most common fluoroelastomers varies between 66 and 70%. As noted above, the failure rate of fluoroelastomer seals in pumps used to pump zero trans-fat oils is unacceptably high.
The fluoroelastomer lip seals are failing in a timeframe as little as six months when used with zero trans-fat oils. The failure is due to tearing of the fluoroelastomer material as the oil “varnishes” out onto the shaft thereby causing the seal to stick and then abrade away in a short period of time. Therefore, new pumps and new seals for use in pumps are needed for reliably pumping zero trans-fat oils.